Nitric oxide (NO) is a gaseous inorganic radical, which freely diffuses in plasma membrane in a living organism, and functions as an intracellular or intercellular signaling factor.
To the present, the biological action of NO has been widely studied from various aspects, and elucidated to cover a broad range of control of vascular function, function as a neurotransmitter, biological defense systems such as inflammatory response and immunological response and the like, and the like. On the other hand, for the disease state of infection or inflammation, NO becomes a major cause of cell and/or tissue damage via oxidation and nitration reaction of biological molecules of protein, nucleic acid and the like due to active nitric-oxide species derived from NO.
Recently, various NO donors have been developed and used as clinical pharmaceutical agents based on various such physiological activities of NO. In fact, S-nitroso glutathione (hereinafter GS-NO), which is a small nitrosothiol, is known to inhibit platelet aggregation but not decrease blood pressure, and applied as a platelet aggregation inhibitor for percutaneous transluminal coronary angioplasty (PTCA) and for the treatment of preeclampsia of pregnant women.
In addition, the active nitric-oxide species derived from NO is also known to have antimicrobial property, and, for example, GS-NO is known to have an antimicrobial activity. However, the antimicrobial activity of small nitrosothiols such as GS-NO is observed only at a high concentration of a few millimolars, and they are associated with insufficient aspects and many problems as a NO donor, such as short blood half life and an adverse influence exerted by a by-product generated simultaneously with NO release.
Incidentally, there are many reports on nitrosylated polymers as well, and, for example, Stamler. J. S. et al (WO96/30006, WO97/10265) have reported on the usefulness of nitrosylated proteins such as nitrosylated hemoglobin. However, inconsistent introduction rate of nitroso group into the protein can be easily anticipated because the proteins they used have plural cysteine residues. Moreover, the problems are feared that hemoglobin itself may act on vascular endothelial cells adversely, may lower renal function by deposition of iron component in the kidney tissue, and the like.
As other nitrosylated proteins, a nitrosylated form (hereinafter S—NO-α1-PI) of α1-protease inhibitor (hereinafter α1-PI) known as a major serine protease inhibitory protein in human serum has been reported (JP-A-11-147838, Y. Miyamoto, T. Akaike, H. Maeda, Biochimica Biophysica Acta, 1477, p. 90–97, (2000)). It has been reported that this S—NO-α1-PI shows an antimicrobial effect at a few micromolars and shows about 1000 times stronger antimicrobial activity as compared to that of GS-NO and the like.
Meanwhile, human serum albumin (HSA) is a major protein present in adult sera, which is produced by the liver and which functions as a carrier transporting various serum molecules. In addition, albumin plays an important role in maintaining the plasma oncotic pressure normally created by a solute (colloid) incapable of passing through capillary pores, thus maintaining the liquid content of blood. Thus, albumin is used for various treatments of conditions involving loss of liquid from blood vessels, such as surgical operation, shock, burn, hypoproteinemia causing edema and the like.
Stamler et al found nitrosylated albumin present in human plasma at the order of μM, and reported that hemoglobin cysteine residue in blood was nitrosylated. From these findings, nitrosylation of protein in living organisms is considered to be related to transportation and storage of NO and control physiological activity of NO (Stamler J. S. et al., Proc Natl Acad Sci USA, 89, p. 7674–7677, (1992), Lia J et al., Nature, 380, p. 221–226, (1996)).
Therefore, a nitrosylated form of albumin, which is present in the largest amount of the serum proteins and which plays a key role in living organisms is highly useful, and supply of stable nitrosylated albumin in clinical situations is significantly important. However, the reactivity of SH group of albumin is markedly lower than that of α1-PI and the like, and artificial and efficient nitrosylation of albumin has not been available.